It is desirable to use production methods that remove or inactivate any infectious agents that accidentally make their way into the starting material of human or animal origin used to prepare vaccines and other biologicals. Pilot studies, conducted under conditions that are easier to control than those in actual production, do not address a practical problem: contaminated starting material or agent adherent to reused equipment or regenerated filtration or ion-exchange media might be accidentally reintroduced into a final product. To prevent that from happening great care must be taken to decontaminate work surfaces, equipment and media effectively. Little is known about inactivation of the highly resistant agents of transmissible spongiform encephalopathies (TSEs) on surfaces or their removal from surfaces. Limited data suggest that drying of the TSE agents protects them from inactivation. We propose to optimize and validate a method to study the inactivation of TSE agents dried onto surfaces or removal of agent from those surfaces.